1. Field of the Invention
This invention relates to apparatus for monitoring a line boundary for determining the validity of a particular "shot" of a ball, and, more particularly, to apparatus for determining the validity of a kill shot in racketball or handball or the like.
2. Description of the Prior Art
U.S. Pat. No. 3,810,148 discloses indicator apparatus for detecting and indicating the presence of an object, such as a ball, on a line or a boundary, such as a boundary line of a tennis court. A pulsed beam of light is transmitted along one side of a line or boundary being monitored. The beam of light is sensed by a receiver. An alarm detects interruptions of a pulsed beam. A second pulsed beam of light is sent along the path adjacent to, and on the other side of, the boundary, and parallel to the first beam of light. Both beams are sensed, and an alarm is energized if either or both of the beams is interrupted. One of the beams may be stylized as the "in" beam and the other beam as the "out" beam. Thus, if the "in" beam is interrupted before the "out" beam, by a tennis ball, the particular shot is a good or valid shot. However, if the "out" beam is interrupted without a corresponding interruption of the "in" beam, then the shot is a bad shot.
In the sport of bowling, light beams have been used to detect the intrusion of a bowler's foot across the flow line. Generally, one or more beams of light are used, with the beams of light being parallel to each other and disposed across an alley and thus perpendicular to the movement of the bowler as he approaches the foul line in the delivery or rolling of a ball. Such apparatus are shown in U.S. Pat. Nos. 2,455,909, 2,650,095, 2,683,602, 3,170,689, and 3,369,810.
The patents discussed in the preceding paragraphs are generally concerned with the interruption of one or more beams of light which are generally parallel to each other and aligned so as to detect the movement of a ball or a foot in a single direction or plane. However, in a game such as handball or racketball, where a front wall, two side walls, and a floor are all involved in playing, the sequential contact of a ball with the side walls, the front wall, and the floor is of primary importance in determining whether a kill shot is valid or invalid. Kill shot, by definition, is a valid shot that strikes the juncture of the front wall and floor simultaneously. Heretofore, such determination has been made on the basis only of visual sightings. Obviously, when only visual sightings are used, there may be differences of opinion as to whether a shot was a good or valid shot or whether it was an invalid shot. For example, if the ball contacts the floor before contacting the front wall, then the shot is invalid and no good. On the other hand, if the shot contacts the front wall before contacting the floor, then the shot is good.
The apparatus of the present invention includes elements for determining the sequence of a ball in contacting the front wall and the floor and accordingly determines the validity or invalidity of a particular shot during a game. An audible signal or a visual signal, or both, may accompany an invalid shot so as to alert the players and officials, if any, about the invalid shot.